With a first-time feature filmmaker and a cast little-known outside Central America, Focus Features will face a considerable challenge appealing to both the art house and Spanish-speaking markets when it releases the film in March.

An extended opening sequence set in the southern Mexican city of Tapachula tracks young gangbanger Casper (Edgar Flores) as he introduces preteen recruit Smiley (Kristyan Ferrer) to the hardcore Mara Salvatrucha syndicate with an initiation beating ordered by jefe Lil' Mago (Tenoch Huerta Mejia).

Meanwhile, in neighboring Honduras, teenager Sayra (Paulina Gaitan) is reunited with her father, who's returned from the U.S. to help her and his brother make the arduous overland journey across Mexico and on to the Texas border, en route to New Jersey.

After Lil' Mago inadvertently kills Casper's girlfriend in a botched rape attempt, he decides to test Casper's loyalty at the Tapachula train yard, where Sayra has arrived with her family to hop a northbound freight. With Smiley in tow, the gangsters begin robbing the migrants precariously riding atop the train. When Lil' Mago tries to assault Sayra, Casper's repressed rage boils over, and he fatally attacks his boss with a machete.

Throwing the body from the train, Casper unthinkingly sends Smiley back to the gang, a decision that soon has his former compatriots hard on his trail, with Smiley himself resolving to avenge Lil' Mago's murder. Despite warnings from her family members, Sayra cautiously befriends Casper as the two strike out together on a desperate dash for the border.

Developed at the Sundance labs, Fukunaga's culturally specific coming-of-age narrative is replete with fascinating character and location details, from the ornately tattooed gang members to the daily perils of barrio life, and clearly benefits from twisting the standard plot to focus on the immigrants' struggle to simply reach the States. Once the story shifts from character drama to quasi-thriller, however, many of the first act's dramatic underpinnings fall away, sacrificing much of the tension and atmosphere.

It soon becomes apparent, however, that beyond his desire for redemption and self-preservation, Casper shows little individuality aside from his gangster identity. Sayra is thinly sketched throughout, and though the actors gamely attempt to fill in the blanks, there's not much backstory or life experience for the young cast to rely on.

Fukunaga clearly exhibits a flair for spirited storytelling, but when "Sin Nombre" departs from the specifics of its unique world in favor of more conventional genre execution, it leaves the characters and audience adrift.